Material for information recording medium substrate, information recording medium substrate, information recording medium, and method for manufacturing them

Abstract

A method for manufacturing a disklike glass material comprising the successive molding of multiple pieces of disklike glass material from glass melt. Being suppressed variation over time in the concentration of infrared radiation-absorbing ions contained in the glass melt being molded into the pieces of disklike glass material so that the variation in the sheet thickness of the multiple pieces of disklike glass material falls within a range of ±15 percent of a reference value. The reference value being the median between the maximum value and the minimum value of the sheet thickness of 1,000 pieces of the glass material. In the course of molding multiple pieces of disklike glass material comprised of glass containing 0.1 to 100 ppm of infrared radiation-absorbing ions, vaiiation over time in the concentration of the infrared radiation-absorbing contained in the glass melt is suppressed to suppress variation in the sheet thickness of the multiple pieces of sheet like glass material.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims benefit of priority to Japanese Patent Application No. 2007-2151 filed on Jan. 10, 2007, which is expressly incorporated herein by reference in its entirety.TECHNICAL FIELD[0002]The present invention relates to a method for manufacturing a disklike glass material comprised of a glass-based substance, particularly an information recording medium substrate-use glass material; a method for manufacturing an information recording medium-use substrate from this material; and a method for manufacturing an information recording medium using this substrate.BACKGROUND ART[0003]Materials such as glass, crystallized glass, and aluminum are employed in the substrates of information recording media such as the magnetic disks loaded in personal computers, portable digital audio equipment, and car navigation systems. Of these, glass-based materials such as glass and crystallized glass afford the advantages of good resistance to sh...

AI Technical Summary

Benefits of technology

[0036]The present invention provides a method for manufacturing a disklike glass material suited to use as an information recording medium substrate-use material for the mass production of sheetlike information recording medium substrate-use materials of constant thickness, a method for manufacturing an information recording medium-use substrate from the material thus manufactured, and a method for manufacturing an information recording medium.BEST MODE OF IMPLEMENTING THE INVENTION

[0037]The present invention is a method for manufacturing a disklike glass material comprising successively molding multiple pieces of disklike glass material from glass melt.

[0038]In the method for manufacturing a disklike glass material comprising the successive molding of multiple pieces of disklike glass material, the press molding method described in Patent Reference 1 or the floating method described in Patent Reference 2 can be employed as is.

[0039]For example, in press molding, as represented by the method described in Patent Reference 1, glass melt is fed between a lower mold and an upper mold opposed to the lower mold, and the glass melt is press molded to form disklike glass. In this method, disklike glass is obtained by press molding with a lower mold and an upper mold that are maintained at a prescribed temperature. While the interior of the disklike glass is at a temperature higher than the glass transition temperature, the upper mold is separated from the disklike glass to complete press molding. Next, a step can be conducted to reduce the warp of the disklike glass that has been molded by press molding. The step to reduce the warp is desirably completed while the interior of the disklike glass is at a temperature higher than the glass transition temperature. From the perspective of reducing the pressing time, press molding and pressing to remove the warp are desirably completed at a temperature higher than the softening point of the glass. The temperature at which the warp of the glass is reduced is desirably lower than the press molding temperature. Since the various pressing is completed at temperatures that are higher than the glass transition temperature and glass softening point, the glass at the end of the press molding basically retains a shape corresponding to the molding surfaces of the mold even after separation from the mold, while being in a state permitting microdeformation by external forces.

[0040]The time required for press molding is desirably not greater than 2 seconds, preferably not greater than 1.8 seconds. The above-mentioned interior of the glass refers to the main portion of the glass that is covered by an outer layer portion of glass where marked release of heat occurs. The temperature of the interior of the glass affects shape retention and shape deformation properties.

[0041]In the floating method, as represented by the method described in Patent Reference 2, glass melt that has been clarified by heating is fed into a float bath to mold a beltlike glass material (glass ribbon) of prescribed thickness. After being molded into a beltlike glass material, this material is mechanically processed to obtain a disklike glass material. Specifically, the mechanical processing comprises milling, grinding, and polishing. A disklike glass material is obtained through these steps. In the present invention, the thickness of the beltlike glass is rendered constant and disks are cut out of the beltlike glass.

Problems solved by technology

As a result, they determined that variation in the concentration of infrared radiation-absorbing ions contained in the glass material is one cause of the variation in sheet thickness of the material.